Adding herbs like parsley and thyme to your diet might help boost your brainpower, courtesy of apigenin. Apigenin is a flavonoid found in many herbs, including parsley, thyme, and chamomile, and certain other plants like celery and other vegetables.

When researchers applied apigenin to human stem cells in a petri dish, something remarkable happened – 25 days later, the stem cells had turned into neurons (an effect that didn't occur without apigenin).1

The synapses, or connections between neurons, were also "strong and more sophisticated," which is crucial for memory consolidation, learning, and overall brain function.2

The researchers noted that apigenin binds to estrogen receptors, which affect the development, maturation, function, and plasticity of the nervous system. They wrote in the journal Advances in Regenerative Biology:3

" … [B]y simply adding a plant compound called apigenin to human pluripotent stem cells, they become neurons after a few days. We also observed that neurons could make more sophisticated connections among themselves after treatment with this natural compound.

This observation suggests that flavonoids derived from plants can be used as a tool for the production of neurons in a dish.

Moreover, since flavonoids are present at high amounts in some foods, we can speculate that a diet rich in flavonoids may influence the formation of neurons and the way they communicate within the brain."

How Might Apigenin Help Grow New Brain Cells?

The fact that apigenin triggers stem cells to become neurons is quite remarkable. Neurogenesis, or your brain's ability to adapt and grow new brain cells, is known to be influenced by lifestyle factors, including exercise and diet.

Apigenin may be one factor in the latter and may explain why flavonoid-rich foods are associated with neurogenesis. According to Stanford University, antioxidants such as flavonoids promote neurogenesis not only in a petri dish but also in rodent brains.

Flavonoids, in particular, increase neurogenesis in the hippocampus of stressed rats, possibly by increasing blood flow to the brain and/or increasing levels of brain-derived neurotrophic factor (BDNF).4 BDNF is a remarkable rejuvenator in several respects.

In your brain, BDNF not only preserves existing brain cells,5 it also activates brain stem cells to convert into new neurons and effectively makes your brain grow larger.

Apigenin May Fight Cancer Too

Brain health isn't the only reason to include more apigenin-rich foods in your diet; it also appears to be a potent cancer fighter. When mice implanted with cells of a particularly deadly, fast-growing human breast cancer were treated with apigenin, the cancerous growth slowed and the tumors shrank.6

Blood vessels feeding the tumors also shrunk and restricted nutrient flow to the tumor cells, starving them of the nutrients need to spread. In 2013, apigenin was again shown to block the ability of breast cancer cells to inhibit their own deaths.

Interestingly, the compound was also found to bind to 160 proteins in the human body, which suggests it has far-reaching health effects (unlike pharmaceutical drugs, which typically only have one specific target). The researchers explained:7

"… [I]n contrast to small-molecule pharmaceuticals designed for defined target specificity, dietary phytochemicals affect a large number of cellular targets with varied affinities that, combined, result in their recognized health benefits."

Apigenin has even been found to make treatment with the breast cancer drug paclitaxel more effective.8 And according to the International Journal of Oncology:9

"Apigenin has been shown to possess remarkable anti-inflammatory, antioxidant, and anti-carcinogenic properties. In the last few years, significant progress has been made in studying the biological effects of apigenin at cellular and molecular levels."

You Can Increase Your Apigenin Intake by Eating Celery, Parsley, and More

Apigenin is most prevalent in celery and parsley, but it's also found in many other plant foods, including:

Apigenin may even be one reason why drinking chamomile tea has been found to reduce thyroid cancer risk by up to 80 percent.10

Human exposure to apigenin occurs mostly through the consumption of apigenin-containing fruits and vegetables, although researchers are not sure how much is absorbed into the bloodstream.

Some of the research studies used an injection of apigenin, but you also obtain biologically significant quantities through a healthy diet. Researchers of the 2011 study noted:11

" … [I]t appears that keeping a minimal level of apigenin in the bloodstream is important to delay the onset of breast cancer …

It's probably a good idea to eat a little parsley … every day to ensure the minimal amount. However, you can also find this compound in pill supplements …"

Turmeric: A Spice with Brain-Boosting, Cancer-Fighting Potential

The plant world is teeming with ingredients that can support your health. Another food worth mentioning is turmeric, whose active ingredient, curcumin, is beneficial for both brain health and cancer prevention/treatment, much like apigenin.

Curcumin has potent anti-cancer properties and is also capable of crossing the blood-brain barrier, which is one reason why it holds promise as a neuroprotective agent in a wide range of neurological disorders.

Researchers have previously investigated curcumin for its potential role in improving Parkinson's, Alzheimer's disease, and stroke damage. It can also promote brain health in general, courtesy of its potent antioxidant and anti-inflammatory properties.

One of the ways it works, which is similar to vitamin D, is by modulating large numbers of your genes. But unlike vitamin D that influences thousands of genes, curcumin has been shown to influence about 700 genes.

Another bioactive compound in turmeric called aromatic-turmerone can increase neural stem cell growth in the brain by as much as 80 percent at certain concentrations.12 Neural stem cells differentiate into neurons and play an important role in self-repair.

The findings suggest aromatic-turmerone may help in the recovery of brain function in neurodegenerative diseases such as Alzheimer's and stroke — provided the effect also applies to humans.

Previous research has also shown that curcumin may help inhibit the accumulation of destructive beta-amyloids in the brain of Alzheimer's patients, as well as break up existing plaques.

Ashwagandha for Your Brain

Another lesser-known herb (at least in the U.S.) is ashwagandha, a small evergreen perennial herb that's been a part of India's Ayurvedic medical system for thousands of years.

While often regarded as an herb for stress reduction and improved energy and vitality, researchers at the National Brain Research Centre (NBRC) have conducted studies on mice that suggest ashwagandha extract may reverse memory loss and improve cognitive abilities in those with Alzheimer's disease.13

Initially, mice with Alzheimer's were unable to learn or retain what they learned, but after receiving ashwagandha for 20 days this improved significantly. After 30 days, the behavior of the mice returned to normal. Researchers reported a reduction in amyloid plaques (amyloid plaques, along with tangles of nerve fibers, contribute to the degradation of the wiring in brain cells) and improved cognitive abilities.

Rather than impacting the brain directly, researchers found that the herb worked by boosting a protein in the liver, which enters the bloodstream and helps clear amyloid from the brain. Researchers concluded, "The remarkable therapeutic effect of W. somnifera [ashwagandha] ... reverses the behavioral deficits and pathology seen in Alzheimer's disease models."

Ginseng and Green Tea: Two More Brain-Boosting Compounds

American ginseng is another beneficial herb that's been linked to improved mental performance. For instance, American ginseng was found to improve working memory and mood in both young individuals and middle-age adults.14 Another study revealed "robust working memory enhancement following administration of American ginseng."15Green tea shows promise for protecting brain health.

In a study presented at the 2015 International Conference on Alzheimer's and Parkinson's Diseases, those who drank green tea one to six days a week had less mental decline than those who didn't drink it.16 Green tea isn't actually an herb, it (as well as black, oolong, dark, and white teas) comes from an evergreen called Camellia sinensis.

What Are Other Top 'Brain Foods?'

If you want to boost your brainpower, one of the best choices you can make is to eat more real foods. Inside healthy foods are the vitamins, minerals, antioxidants, and countless other phytochemicals to nourish your brain cells (and even grow new ones).

Consider this: people who eat plenty of vegetables and fruits (about 1.6 cups, or 400 grams) a day perform better on cognitive tests,17 while those who eat a lot of sugar are 1.5 times more likely to develop mild cognitive impairment than those who do not.18

Celery may be particularly beneficial, as in addition to containing apigenin, it's also a rich source of luteolin, a plant compound that may calm inflammation in your brain, which is a primary cause of neurodegeneration. Luteolin has also been linked with lower rates of age-related memory loss in mice, and older mice fed a luteolin-supplemented diet scored better on learning and memory tasks.19 In addition to celery, peppers and carrots are also good sources of luteolin.

The omega-3 fats found in wild Alaskan salmon are also important, as they help fight inflammation throughout your body, including in your brain, and offer numerous protections to your brain cells.

For instance, a study in the journal Neurology found "older women with the highest levels of omega-3 fats … had better preservation of their brain as they aged than those with the lowest levels, which might mean they would maintain better brain function for an extra year or two."20

In separate research, when boys were given an omega-3 supplement, there were significant increases in the activation of the dorsolateral prefrontal cortex part of the brain.21 This is an area of your brain that is associated with working memory. They also noticed changes in other parts of the brain, including the occipital cortex (the visual processing center) and the cerebellar cortex (which plays a role in motor control).

You can get omega-3 fats in therapeutic doses by taking a supplement like krill oil. But, if you're looking for a food source, wild Alaskan salmon (along with sardines and anchovies) is among the best. Keep in mind that your brain is not "programmed" to shrink and fail as a matter of course as you age. In fact, you can build a bigger, better brain by making smart choices, including fortifying your diet with herbs, vegetables, and healthy fats.